1. Field of the Invention
This invention involves generally devices for converting electrical power to mechanical power and more particularly involves a motor that exploits the changes in pressure induced by the electrochemical pumping of an electrochemically active gas through an electrolytic membrane.
2. Description of the Related Art
An electrochemical cell is typically formed by positioning an electrolytic membrane between and in contact with a cathode and an anode. Such a cell can either generate electricity (chemical to electrical) or do mechanical work (electrical to mechanical). When the cell is configured as a `fuel cell` to generate electricity, a fuel gas such as hydrogen is supplied to the anode and a gaseous oxidant such as oxygen is supplied to the cathode. When the cell is configured as a motor to produce mechanical energy, an electrical voltage is applied across the anode and cathode, and an electrochemically active gas (capable of entering into an oxidation/reduction reaction) is supplied to the anode. At the anode, the gas is ionized and the ions travel across the electrolytic membrane in response to the voltage gradient across the membrane. At the cathode, the ions are reconverted to molecules of the gas, thereby increasing the pressure on the cathode side and decreasing the pressure on the anode side of the membrane. The result is a pumping action across the membrane from anode to cathode. U.S. Pat. No. 4,402,817 issued to Henri J. R. Maget on Sept. 6, 1983 discloses such a single cell used as a prime mover.
U.S. Pat. Nos. 4,522,698 and 4,648,955 issued to Henri J. R. Maget on Jun. 11, 1985 and Mar. 10, 1987, respectively, disclose improvements in the application of an electrochemical cell for the production of mechanical energy. Practitioners in the art continue to search for more efficiency and lower cost in mechanical energy sources (motors) as well as more flexible control characteristics such as high-frequency motion modulation and positioning precision. For many applications, practitioners turn to the standard electrical motor or solenoid, both well-known in the art, but the electrochemical motor may be more useful for applications requiring low power, high precision, and small size. U.S. Pat. 4,902,278 issued to H. J. R. Maget et al. on Feb. 20, 1990 is exemplary of the special usefulness of the electrochemical motor in applications where the electrical solenoid or rotary motor cannot be used. The absence of moving parts permits an embodiment of the electrochemical motor to be implanted within the human body according to the teachings of U.S. Pat. No. 4,902,278.
Energy efficiency is an important characteristic of direct current (DC) electrical-mechanical converters. Electrochemical motors, like fuel cells, become more efficient as the applied load decreases because a fixed threshold-excitation energy is not required. Electromechanical motors become less efficient as the load decreases, but can support increased loads with small incremental increases in energy. Other advantages of the electrochemical motor include the absence of geometric interdependence of the component parts. Accordingly, the design of an electrochemical motor is amenable to unusual geometries for size and shape where the designs of conventional electromechanical motors and solenoids are limited by the necessary interaction among the moving parts. Although electrochemical motors may be readily microminiaturized for low power requirements, large mechanical loads may require the use of cell stacks, which will eventually, with increasing capacity, become more complex than an electromechanical motor of equivalent capacity.
The electrochemical motor can operate over a wide dynamic range (e.g. 250 to 1) with precision unavailable in an electromechanical motor, which tends to stall at low speeds. An electrochemical motor may be reversed instantaneously and without the inertial slippage caused by the momentum of moving parts.
Accordingly, as is known in the art, there are many requirements for the features available from a typical electrochemical motor and a need for improved electrochemical motor performance characteristics. The most important of these include high energy efficiency, control precision, capacity for rapid modulation, and integrated sensing and feedback features to permit fully automatic stored-program control.